1. Field of the Invention
The present disclosure generally relates to seat belts, and otherwise restraining straps that experience tensile loads in use. More particularly, the invention concerns a belt or strap that utilizes active material actuation to selectively modify tension therein.
2. Discussion of Prior Art
The use of seat belts and otherwise restraining straps (i.e., collectively referred to herein as “restraining belts”) are widely used in various arts for securing occupants and/or cargo. In a vehicular setting, for example, these safety devices typically include a flexible planar member (e.g., webbing) operable to sustain a tensile load when serving as a restraint, a clasp or fastener (e.g., buckle) for fixing the restraint, and a retractor operable to tension the belt once applied as a restraint. The retractor is typically configured to automatically lock upon a sudden stop or crash event by a pendulum and locking bar that engages an otherwise spring biased sprocket coupled to the webbing.
Concernedly, and with respect to the present invention, conventional restraining belts typically provide a constant magnitude of tension. During a crash event, for example, a normally suitable amount of tension generated by the locked retractor may cause greater peak forces to be transferred to the occupant or cargo through the webbing. FIG. 1 presents an exemplary load versus payout (i.e., rate of dispensing belt webbing) graph during such an event. As a result, load limiting retractors have been developed to limit the achievable tensile loads on the belt and therefore, the transferable peak forces upon the occupant. However, these retractors also present various concerns in the art. For example, and as shown in FIG. 2, once triggered, conventional load limiting devices typically produce an instantaneous and constant limited load. Moreover, these types of retractors often employ complex electro-mechanical actuators that increase operational, energy consumption, and repair/maintenance costs.